BASE STATION EQUIPMENT USING DIVERSITY RECEPTION

Abstract: A base station in a duplex radio communication system comprises two transceivers (10, 12) each of which has a transmitter (14, 20), a main receiver (16, 22) and a diverse receiver (18, 24). A main antenna (26) is connected to the common port of a first diplex filter (38), and a diverse antenna (28) is connected to the common port of a second diplex filter (40). A first amplifier and splitter (30, 32) feed main receive signals from the main antenna (26) to the main receivers (16, 22) and a second amplifier and splitter (34, 36) feed diverse receive signals from the diverse antenna (28) to the diverse receivers (18, 24). The diverse antenna (28) acts not only as a receive antenna, but also transmits signals from the transmitter (20), so more power is available for transmission.

Description: Base Station Equipment Using Diversity Reception This invention relates to radio communication systems. Base stations for duplex radio communication, such as for GSM (Group Systeme Mobile) cellular systems, commonly use a single antenna for transmission and reception of radio signals where the transmit and receive radio signals have separate and distinct frequency allocations by utilising a diplex filter to separate the frequencies of the transmitted and received signals. This is illustrated in Figure 1 of the accompanying drawings. When a second carrier signal is required to be transmitted using the same frequency allocation as the first signal described above and using the same antenna it is common practice to utilise a 3dB combiner to connect the two signals to the same antenna, as illustrated in Figure 2 of the accompanying drawings. This method of combination limits the production of intermodulation products which might interfere with the reception of wanted signals. Typically more than half of the power of each signal is dissipated in the 3 dB combiner and is not usefully transmitted which results in a reduced range of effective communication. This is typically overcome by increasing the power of each signal to allow for the power dissipated in the combiner or accepting a reduced size of cell, ie the area covered by the transmitter. This invention provides a way of utilising elements typically used in a duplex communication system to provide low loss combination of two transmit signals over a broad band of frequencies. This allows more efficient use of generated signal power which permits either greater range of effective communication with existing generated power and thus requiring fewer transmitters to cover a given area, or reduced generated power for the same area coverage thus requiring less energy and less costly transmitter design. A second antenna sited near to but separate from the main antenna is commonly connected to a second receiver to provide a second diverse, received signal which when considered in addition to the main received signal increases the likelihood of having adequate reception. Figure 3 shows a known system employing such antenna diversity. According to the invention a duplex radio communication system comprises a first transceiver having a first transmitter, a second transceiver having a second transmitter, a first filter connected to a main antenna and a second filter connected to a diverse antenna providing diversity of the received signal, the first filter supplying transmit signals from the first transmitter to the main antenna and the second filter supplying transmit signals from the second transmitter to the diverse antenna. Preferably, the first filter supplies, through a first amplifier and power splitter, a main receive signal to respective main receivers in the first and second transceivers, and the second filter supplies, through a second amplifier and power splitter, a diverse receive signal to respective diverse receivers in the first and second transceivers. The principle of this invention is to transmit the two signals without losing useful power in a broadband 3dB combiner. This is done by using a diplex filter to apply the second signal to be transmitted to the diverse antenna which is commonly used for reception only. The loss in the diplex filter is typically less than the loss in the 3dB combiner and so more power is available for transmission in the antenna. Also since the two transmitted signals are not present in the same signal path of the transmitting equipment there is less opportunity f.or intermodulation products to be generated. The invention will now be further described with reference to Figure 4 of the accompanying drawings which shows a block circuit diagram of a preferred duplex radio communicaion system in accordance with the present invention. The system of Figure 4 is incorporated in a base station and has two transceivers 10, 12 operating in TDMA (time- division multiple access). The TDMA system architecture conforms to the GSM standard, using eight time slots per frame, the transmission rate therefore being eight times the coding rate. The transceivers 10 and 12 operate at different frequencies but with their transmit and receive slots in synchronism. The transceiver 10 has a transmitter 14, a main receiver 16 and a diverse receiver 18. Similarly, the transceiver 12 has a transmitter 20, a main receiver 22 and a diverse receiver 24. The system has a main antenna 26 and a diverse antenna 28 for radio communication with mobile handsets. A main receive path includes a first amplifier 30 and power splitter 32, and a diverse receive path includes a second amplifier 34 and power splitter 36. The transmit signal from the transmitter 14 to the antenna 26, and the main receive signal from the antenna 26, pass through a first diplex filter 38. Similarly, the transmit signal from the transmitter 20 to the antenna 28, and the diverse receive signal from the antenna 28, pass through a second diplex filter 40. Hence, the diverse antenna 28 is employed also as a transmitter. In the case of a multi-sector cell, the system of Figure 4 is repeated for each cell.

Claims: Claims 1. A duplex radio communication system comprising a first transceiver having a first transmitter, a second transceiver having a second transmitter, a first filter connected to a main antenna and a second filter connected to a diverse antenna providing diversity of the received signal, the first filter supplying transmit signals from the first transmitter to the main antenna and the second filter supplying transmit signals from the second transmitter to the diverse antenna. 2. A duplex radio communication system according to claim 1, wherein the first filter supplies, through a first amplifier and power splitter, a main receive signal to respective main receivers in the first and second transceivers, and the second filter supplies, through a second amplifier and power splitter, a diverse receive signal to respective diverse receivers in the first and second transceivers. 3. A duplex radio communication system according to claim 1 or 2, wherein the first filter and the second filter take the form of diplex filters. 4. A duplex radio communication system according to any of the preceding claims and constituting a base station capable of communicating with mobile handsets in a radio telephone system.

Inventors: LAWRENCE THOMAS WILLIAM JOHN, LAWRENCE, THOMAS, WILLIAM, JOHN
Applicants: LAWRENCE THOMAS WILLIAM JOHN, NOKIA TELECOMMUNICATIONS OY, LAWRENCE, THOMAS, WILLIAM, JOHN
Application year: 1994
Main classification: H04B7
IPC codes: H04B7, H04Q7